//
//  Copyright 2009 Vadim Ushakov
// 
//  This program is free software; you can redistribute it and/or modify it
//  under the terms of the GNU General Public License as published by the Free
//  Software Foundation; either version 2 of the License, or (at your option)
//  any later version.
// 
//  This program is distributed in the hope that it will be useful, but
//  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
//  or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
//  for more details.
//  
//  You should have received a copy of the GNU General Public License along
//  with this program; if not, write to the Free Software Foundation, Inc.,
//  59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
//
//  This program includes Mersenne Twister random number generator
//  implementation, coded by Takuji Nishimura and Makoto Matsumoto.
//  The original sources can be found at http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
//  and are available under the following license:
//  
//  Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
//  All rights reserved.                          
//  
//  Redistribution and use in source and binary forms, with or without
//  modification, are permitted provided that the following conditions
//  are met:
//  
//    1. Redistributions of source code must retain the above copyright
//       notice, this list of conditions and the following disclaimer.
//  
//    2. Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//  
//    3. The names of its contributors may not be used to endorse or promote 
//       products derived from this software without specific prior written 
//       permission.
//  
//  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
//  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
//  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
//  A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
//  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
//  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
//  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
//  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
//  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
//  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
//  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
//  
//  

#include "kernelRandom.h"
#include "kernelError.h"
#include "kernelLog.h"
#include "kernelRtc.h"
#include "kernelSysTimer.h"


// Entropy pool

#define ENTROPY_POOL_SIZE 47
static volatile unsigned kernelEntropyPool[ENTROPY_POOL_SIZE];
static volatile unsigned kernelEntropyPoolReadIndex;
static volatile unsigned kernelEntropyPoolWriteIndex;

// Mersenne Twister generator pool

#define N 624
#define M 397
#define MATRIX_A 0x9908b0dfUL   /* constant vector a */
#define UPPER_MASK 0x80000000UL /* most significant w-r bits */
#define LOWER_MASK 0x7fffffffUL /* least significant r bits */

static unsigned long mt[N]; /* the array for the state vector  */
static int mti=N+1; /* mti==N+1 means mt[N] is not initialized */ 

/* initializes mt[N] with a seed */
static void init_genrand(unsigned long s)
{
	mt[0]= s & 0xffffffffUL;
	for (mti=1; mti<N; mti++)
	{
		mt[mti] =  (1812433253UL * (mt[mti-1] ^ (mt[mti-1] >> 30)) + mti); 
		/* See Knuth TAOCP Vol2. 3rd Ed. P.106 for multiplier. */
		/* In the previous versions, MSBs of the seed affect   */
		/* only MSBs of the array mt[].                        */
		/* 2002/01/09 modified by Makoto Matsumoto             */
		mt[mti] &= 0xffffffffUL;
		/* for >32 bit machines */
	}
} 

/* generates a random number on [0,0xffffffff]-interval */
static unsigned long genrand(void)
{
	unsigned long y;
	static unsigned long mag01[2]={0x0UL, MATRIX_A};
	/* mag01[x] = x * MATRIX_A  for x=0,1 */

	if (mti >= N) /* generate N words at one time */
	{
		int kk;

		if (mti == N+1)             /* if init_genrand() has not been called, */
			init_genrand(5489UL); /* a default initial seed is used */

		for (kk=0;kk<N-M;kk++)
		{
			y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
			mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & 0x1UL];
		}
		for (;kk<N-1;kk++)
		{
			y = (mt[kk]&UPPER_MASK)|(mt[kk+1]&LOWER_MASK);
			mt[kk] = mt[kk+(M-N)] ^ (y >> 1) ^ mag01[y & 0x1UL];
		}
		y = (mt[N-1]&UPPER_MASK)|(mt[0]&LOWER_MASK);
		mt[N-1] = mt[M-1] ^ (y >> 1) ^ mag01[y & 0x1UL];

		mti = 0;
	}
  
	y = mt[mti++];

	/* Tempering */
	y ^= (y >> 11);
	y ^= (y << 7) & 0x9d2c5680UL;
	y ^= (y << 15) & 0xefc60000UL;
	y ^= (y >> 18);

	return y;
}

/////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////
//
//  Below here, the functions are exported for external use
//
/////////////////////////////////////////////////////////////////////////
/////////////////////////////////////////////////////////////////////////


int kernelRandomInitialize(void)
{
	int status = 0;
	unsigned long v = 0;

	v = kernelRtcReadHours();
	v = v * 60 + kernelRtcReadMinutes();
	v = v * 60 + kernelRtcReadSeconds();
	v += kernelGetMicrosecondSoftTimer();

	init_genrand(v);

	return (status);
}


unsigned kernelRandomUnformatted(void)
{
	// This is for getting an unformatted random number.
	return genrand() ^ kernelReadEntropyRandom();
}


unsigned kernelRandomFormatted(unsigned start, unsigned end)
{
	// This function will return a random number between "start" and "end".

	unsigned limit = 0;

	unsigned v = kernelRandomUnformatted();

	if (end == start)
		// Ok, whatever
		return (end);

	if (end < start)
	{
		kernelError(kernel_error, "end (%u) < start (%u)", end, start);
		return (start);
	}

	limit = ((end - start) + 1);
	if (!limit)
		limit = ~0U;

	return ((v % limit) + start);
}


unsigned kernelRandomSeededUnformatted(unsigned seed __attribute__((unused)))
{
	return kernelRandomUnformatted();
}


unsigned kernelRandomSeededFormatted(unsigned seed __attribute__((unused)), unsigned start, unsigned end)
{
	return kernelRandomFormatted(start, end);
}


void kernelSendEntropyValue(unsigned v)
{
	unsigned i = (kernelEntropyPoolWriteIndex++) % ENTROPY_POOL_SIZE;
	kernelEntropyPool[i] += v;
}


unsigned kernelReadEntropyRandom(void)
{
	unsigned result = 0;
	unsigned k = (kernelEntropyPoolReadIndex++) % ENTROPY_POOL_SIZE;
	unsigned i;

	for (i = 0; i < ENTROPY_POOL_SIZE / 2; i++)
	{
		result += kernelEntropyPool[(i + k) % ENTROPY_POOL_SIZE];
		i++;
		result ^= kernelEntropyPool[(i + k) % ENTROPY_POOL_SIZE];
	}

	return (result);
}

